Abstract: Based on the modular design thought, two drilling rigs for difficult geological conditions of coal mine were designed with drilling ability of 300 m to prevent water disaster effectively, the one named ZDY3500T adopts separated type and the other named ZDY3500LT adopts track type. This article sketched rotary device, feeding device, clamping mechanism, hydraulic system, power pumps and safety device of the wellhead. These two rigs can adapt to different well types, and meet the needs of different types of water exploration and drainage borehole construction.